Sectional view of a flywheel storage with magnetic bearings and evacuated housing A flywheel-storage power system uses a

flywheel A flywheel is a mechanical device which uses the conservation of angular momentum to store rotational energy; a form of kinetic energy proportional to the product of its moment of inertia and the square of its rotational speed. In particular, ass ...

for energy storage, (see

Flywheel energy storage Flywheel energy storage (FES) works by accelerating a rotor (flywheel) to a very high speed and maintaining the energy in the system as rotational energy. When energy is extracted from the system, the flywheel's rotational speed is reduced as a c ...

) and can be a comparatively small storage facility with a peak power of up to 20 MW. It typically is used to stabilize to some degree power grids, to help them stay on the grid frequency, and to serve as a short-term compensation storage. Unlike common storage power plants, such as the pumped storage power plants with capacities up to 1000 MWh, the benefits from flywheel storage power plants can be obtained with a facility in the range of a few kWh to several tens of MWh. They are comparable in this application with battery storage power plants. Possible areas of application are places where electrical energy can be obtained and stored, and must be supplied again to compensate for example, fluctuations in the seconds range in wind or solar power. These storage facilities consist of individual flywheels in a modular design. Energy up to 150 kWh can be absorbed or released per flywheel. Through combinations of several such flywheel accumulators, which are individually housed in buried underground vacuum tanks, a total power of up to several tens of MWh can be achieved. The electrical connections power low voltage motors via a DC intermediate circuit and the power converter systems are comparable to those found in plants used in the high-voltage direct current transmissions application. Sometimes

battery storage power station A battery storage power station is a type of energy storage power station that uses a group of batteries to store electrical energy. Battery storage is the fastest responding dispatchable source of power on electric grids, and it is used to sta ...

s are built with flywheel storage power systems in order to conserve battery power. Flywheels can handle rapid fluctuations better.

Application examples

Vehicle braking and acceleration

In vehicles small storage of power flywheels are used as an additional mechanism with batteries, to store the braking energy by regeneration. Power can be stored in the short term and then released back into the acceleration phase of a vehicle with very large electrical currents. This conserves battery power.

Tram braking and acceleration – power smoothing

Flywheel storage has proven to be useful in

trams A tram (called a streetcar or trolley in North America) is a rail vehicle that travels on tramway tracks on public urban streets; some include segments on segregated right-of-way. The tramlines or networks operated as public transport are ...

. During braking (such as when arriving at a

station Station may refer to: Agriculture * Station (Australian agriculture), a large Australian landholding used for livestock production * Station (New Zealand agriculture), a large New Zealand farm used for grazing by sheep and cattle ** Cattle statio ...

), high energy peaks are found which can not be always fed back into the power grid due to the potential danger of overloading the system. The flywheel energy storage power plants are in containers on side of the tracks and take the excess electrical energy. For example, up to 200 MWh energy per brake system is annually recovered in

Zwickau Zwickau (; is, with around 87,500 inhabitants (2020), the fourth-largest city of Saxony after Leipzig, Dresden and Chemnitz and it is the seat of the Zwickau District. The West Saxon city is situated in the valley of the Zwickau Mulde (German: ' ...

Power grid frequency control

Stephentown, New York Stephentown is a town in Rensselaer County, New York, United States. The population was 2,903 at the 2010 census. The town, which was originally Jericho Hallow in the Massachusetts Bay Colony, was renamed for Stephen Van Rensselaer. The town is l ...

, Beacon Power operates in a flywheel storage power plant with 200 flywheels of 25 kWh capacity and 100 kWh of power. Ganged together this gives 5 MWh capacity and 20 MWh of power. The units operate at a peak speed at 15,000 rpm. The rotor flywheel consists of wound

CFRP CFRP may refer to: * Carbon fiber reinforced polymer, a material * CFRP-FM CHLC-FM is a Class B FM station broadcasting on the frequency of 97.1 MHz using an omnidirectional antenna. The station has a hot adult contemporary format. CHLC- ...

fibers which are filled with resin. The installation is intended primarily for frequency control. This service is sold to the New York power grid. Stadtwerke München (SWM,

Munich Munich ( ; german: München ; bar, Minga ) is the capital and most populous city of the States of Germany, German state of Bavaria. With a population of 1,558,395 inhabitants as of 31 July 2020, it is the List of cities in Germany by popu ...

Germany Germany,, officially the Federal Republic of Germany, is a country in Central Europe. It is the second most populous country in Europe after Russia, and the most populous member state of the European Union. Germany is situated betwe ...

) uses a flywheel storage power system to stabilize the power grid, as well as control energy and to compensate for deviations from renewable energy sources. The plant originates from the Jülich Stornetic GmbH. The system consists of 28 flywheels and has a capacity of 100 kWh and a capacity of 600 kilovolt-amperes (kVA). The flywheels rotate at a peak speed of 45,000 rpm. In

Ontario Ontario ( ; ) is one of the thirteen provinces and territories of Canada.Ontario is located in the geographic eastern half of Canada, but it has historically and politically been considered to be part of Central Canada. Located in Central Ca ...

Canada Canada is a country in North America. Its ten provinces and three territories extend from the Atlantic Ocean to the Pacific Ocean and northward into the Arctic Ocean, covering over , making it the world's second-largest country by tot ...

, Temporal Power Ltd. has operated a flywheel storage power plant since 2014. It consists of 10 flywheels made of steel. Each flywheel weighs four tons and is 2.5 meters high. The maximum rotational speed is 11,500 rpm. The maximum power is 2 MWh. The system is used for frequency regulation. After a successful three-year trial period, the system is to be expanded to 20 MWh and 100 MWh.

Renewable energy time shift

The city of

Fresno Fresno () is a major city in the San Joaquin Valley of California, United States. It is the county seat of Fresno County and the largest city in the greater Central Valley region. It covers about and had a population of 542,107 in 2020, maki ...

California California is a U.S. state, state in the Western United States, located along the West Coast of the United States, Pacific Coast. With nearly 39.2million residents across a total area of approximately , it is the List of states and territori ...

is running flywheel storage power plants built by Amber Kinetics to store solar energy, which is produced in excess quantity in the daytime, for consumption at night.

Deployed systems

On the island of

Aruba Aruba ( , , ), officially the Country of Aruba ( nl, Land Aruba; pap, Pais Aruba) is a constituent country of the Kingdom of the Netherlands physically located in the mid-south of the Caribbean Sea, about north of the Venezuela peninsula of ...

is currently a 5 MWh flywheel storage power plant built by Temporal Power Ltd. The island intends to convert its energy supply to 100 percent renewables by 2020.

Energy loss

It is now (since 2013) possible to build a flywheel storage system that loses just 5 percent of the energy stored in it, per day (i.e. the self-discharge rate).zdf-video
ZDF Feb 2013 - Planet E - Schwungradspeicher, Minute 24:35 In German

References

{{reflist, colwidth=30em Energy storage Power stations